1. Field of the Invention
The present invention relates to a pretreatment liquid for a recording material and an image recording method using the pretreatment liquid.
2. Discussion of the Background
Recently, inkjet printers have been used very popularly because of being quiet and having low costs. In addition, color inkjet printers which can print color images on a plain paper have also been practically used in the market.
As colorants for inks for office-use inkjet printers, dyes which have high solubility, have been typically used to prevent occurrence of a nozzle-choking problem in that a nozzle of an inkjet printer is choked with a material such-as colorants included in an ink. However, dyes typically have poor resistance to water and light. Therefore inks including a pigment as a colorant have been increasingly used for posters whose images are needed to have good resistance to water and light.
In addition, when color images are printed on a plain paper, an additive such as surfactants is typically used for inks to improve the penetration property of the inks, i.e., to improve blurring of the boundary portion between two or more overlaid color images (hereinafter this blurring is referred to as the image blurring problem). This technique is disclosed, for example, in Japanese Laid-Open Patent Publication No. (hereinafter referred to as JOP) 55-65269. However, even when such inks are used, a feathering problem in that character images and fine line images are blurred cannot be fully solved. Therefore a technique in which an ink having a low penetration property is used for only the black ink in a color ink cartridge is disclosed. However, by using such a technique, the feathering problem cannot be fully solved, and particularly the image blurring problem cannot be fully solved.
In attempting to solve such a problem, JOPs 56-86789, 55-144172, 55-81992, 52-53012 and 56-89594 have disclosed techniques in which a material capable of fixing a dye included in recording inks is previously coated on a recording material or a white pigment or a water-soluble polymer is coated on the surface of a recording material, to fix a dye ink image formed on the recording material. In these techniques, it is needed to use papers which have been subjected to a special treatment.
JOP 56-89595 discloses an inkjet printing method in which a solution of a polymer such as carboxymethyl cellulose, polyvinyl alcohol and polyvinyl acetate is sprayed on a surface of a plain paper and then an ink is sprayed to form an ink image on the polymer-coated area of the plain paper. However, the feathering problem cannot be prevented by such an image forming method, and in addition, the water resistance of the recorded images cannot be improved at all.
JOPs 64-63185, 8-20159 and 8-20161 have disclosed inkjet printing methods in which a pretreatment liquid including a compound capable of insolubilizing a dye included in an ink to be used for printing images is sprayed by an inkjet printing method on a surface of a recording material and then the ink is sprayed on the surface of the recording material. However, these methods have a drawback in that the pretreatment liquid is needed to have a low viscosity to be stable sprayed on the surface of a recording material, namely the content of the dye-insolubilizing compound in the pretreatment liquid has to be decreased, and thereby the image quality improving effect is hardly exerted.
In order to fully exert the image quality improving effect by using such a pretreatment liquid, it is needed to apply a large amount of a pretreatment liquid on a recording material, resulting in occurrence of problems such as curling or cockling of the recording material. In particular, image areas in which two or more color ink images are overlaid include a large amount of water, and therefore an ink-penetrating problem in that the ink images penetrate into a recording material and reach the backside of the recording material occurs as well as the cockling problem of the recording material.
JOP 8-142500 discloses an inkjet printing method in which a colorless liquid including a silicone compound such as silicone oils and a cationic compound is previously coated on a recording material and then a recording ink including an anionic compound is sprayed on the recording material to form an image thereon. However, the silicone-coated surface of the recording material has poor ink permeability and therefore it takes a long time to dry the recorded ink images. In addition, when an image is recorded on such a recording material at a high speed, various problems tend to occur. For example, problems occur such that a dot image tends to be mixed with the neighboring dots because the silicone-coated surface has poor wettability and an undesired white line image is formed in a solid image because a roller contacts the solid image which have not yet dried. Thus image qualities seriously deteriorate. In addition, when such a pretreatment liquid is preserved for a long period of time, the silicone oil included therein decomposes or is separated from the other components, and thereby images having good image qualities cannot be stably produced.
JOP 10-250216 discloses an image recording method in which a colorless or pale-colored record-accelerating liquid including a dye-insolubilizing compound capable of insolubilizing the dye included in a recording ink is applied on a surface of a recording material and then the recording ink is sprayed on the surface of the recording material, wherein the record-accelerating liquid further includes a specific surfactant. According to this image recording method, the surfactant in the record-accelerating liquid improves the permeability and wettability of recording materials, and thereby the recorded images can be rapidly dried, resulting in performance of high speed printing. However, there is a possibility that the colorant in the ink penetrates into the recording paper, resulting in decrease of image density and occurrence of the feathering problem. Therefore, the image recording method is needed to be further improved.
JOP 2000-37942 discloses an image recording method in which a pretreatment liquid including a water-soluble polyvalent metal salt or a polyallylamine in an amount of from 20 to 25% by weight is applied on a surface of a recording material by an inkjet printing method, and then an ink including a pigment as a colorant is sprayed after the recording material applied with the pretreatment liquid is pressed or heated, to form an image on the surface of the recording material. It is described therein that images having good image qualities can be formed on a recording material even when the pretreatment liquid is applied in an amount of 1/10 to ½ of the application amount of a pretreatment liquid in conventional methods including no pressure applying process. In addition, it is also described therein that by pressing a recording material, occurrence of the cockling problem can be prevented. However, in this method an additional process such as pressing processes or heating processes has to be performed, and therefore the printing devices become complex and large in size.
JOPs 11-10856, 2000-44855 and 2000-63719 have disclosed pretreatment liquids including a water-soluble poly-valent metal salt in such a large amount as 35% by weight. These pretreatment liquids are applied on a surface of a recording material by an on-demand inkjet printing method, and therefore the pretreatment liquids have to have a low viscosity. As mentioned above, when pretreatment liquids having a low viscosity are applied on a surface of a recording material, the pretreatment liquid produces little image-quality enhancing effect. In addition, these pretreatment liquids is needed to include a special material such as particulate polymers which typically have high manufacturing costs.
Thus, an inkjet printing method by which images having high image qualities can be recorded at a high recording speed has not yet been realized although various proposals have been made.